Supplement Application for R37: Interstitial fluid flow in Alzheimer?s Disease Progression (Munson, PI) Project Summary Alzheimer?s Disease is a devastating disease marked by cognitive decline. The reasons underlying this decline are still unclear, but it is known that Amyloid ? (A?) aggregation and accumulation in the brain contributes to worsening cognitive deficits. Recently, it has been identified that major mediators of bulk fluid flow in the brain are implicated in the clearing of Amyloid ?, including the glymphatic system, the meningeal lymphatics, and the blood vasculature. Decreased fluid flow via any of these routes can worsen accumulation of A? and cognitive deficits in murine models of the disease. Bulk pathways are important for understanding overall clearance from the brain, however, it does not give us insight into the underlying cellular or tissue-level mechanisms. Interstitial fluid flow is the flow within tissue around the cells, interacting with each cell surface. These interactions can result in downstream changes to cell signaling inducing activation, inflammatory cascades, and cellular migration. In brain cancer, increased interstitial fluid flow develops due to the increase in interstitial pressure in the tumor bulk interfacing with the relatively normal pressure of the surrounding brain tissue, or tumor microenvironment. In our prior grant, we focused on this increased interstitial flow in brain cancer to identify the mechanisms underlying this flow-mediated invasion. To examine how interstitial fluid flow affects the invasion of brain cancer cells, we have developed in vitro and in vivo methods to examine fluid flow responses including multicellular in vitro tissue engineered systems and in vivo imaging methods. In AD, though flow may be decreasing, the same molecules and mechanisms may be involved due to their flow sensitivity. Thus, in this application, we will conduct direct in vivo measurements of interstitial flow using intravital imaging in mouse models of AD. Using this information we will build our in vitro models of the neuro-glial microenvironment with human and mouse healthy and AD-affected cells to identify the role of IFF in secretion, accumulation, and patterning of A? as well as the effect of different types of A? and IFF on cellular health. Last, we will determine the role of a unique molecule identified in cancer but expressed on astrocytes and microglia, S1PR3, in mediating the AD phenotype and determine if there is benefit to therapeutically agonizing or antagonizing this receptor to mitigate cognitive deficits. Altogether, these reports will advance the importance and strategies for mitigating interstitial flow and its effects in Alzheimer?s Disease and offer modalities by which to study further effects of flow at the cellular level. Understanding the impact of interstitial flow may ultimately help predict, diagnose, and treat Alzheimer?s Disease.